Abstract
<p>In this paper, we present the design and testing of a radiofrequency prototype coil with good performances in terms of B<sub>1</sub> magnetic field homogeneity and can be utilized for Magnetic Resonance Imaging. It is constituted of four coaxial separately tuned rings of wire and symmetrically located on a spherical surface. Compared to standard Helmholtz pair, which has 2nd-order magnetic field homogeneity, it yields to improvement in field homogeneity, while preserving the simplicity of design. The four coils of proposed structure are tuned to the same frequency. The proposed structure gets at 4th-order magnetic field homogeneity by optimizing the distance between rings and the diameters of outer loops. An electrical modeling of the four-coil system taking into account the coupling effects between all rings permits to determine the resonance frequency in the homogenous mode. Measurements of B1 field homogeneity were introduced in free space. Compared to the Helmholtz coil, the proposed structure presents good performances in terms of B1 homogeneity, quality factor and sensitivity. The design of proposed coil has been optimized for best SNR performances. Globally, this work claims to be a contribution to the study of the four-coil RF systems derived from the Helmholtz pairs.</p>
Highlights
Radio frequency (RF) coil system (Hayes & Eash, 1985), (Syms & Gilderdale, 2005) is a critical component in a MRI system, which is an electrical device generally composed of multiple wire loops that can either generate a magnetic field or detect a changing magnetic field as an electric current induced in the wire
Much works have shown that the quality of the image obtained by MRI is, in particular, depending on the intensity of the homogeneity of radiofrequency fields (RF) B1T produced by the transmit coil and B1R associated with the receiving coil (Anderson, 1999), (Bongiraud & Jeandey, 1999), (Harpen, 1991), (Mispelter & ANMR, 2006), In general, the homogeneity of the B1 field produced by the RF coils is in multiple radiating elements and their design is constantly optimized
The optimization and electrical modeling of RF coils structures with periodic geometry are the subject of constant research
Summary
Radio frequency (RF) coil system (Hayes & Eash, 1985), (Syms & Gilderdale, 2005) is a critical component in a MRI system, which is an electrical device generally composed of multiple wire loops that can either generate a magnetic field or detect a changing magnetic field as an electric current induced in the wire.A transmit and receive coil can send or transmit a B1 field and receive RF energy from imaged sample. After providing a transmitting excitation RF pulse as, the current source within a RF coil induces a B1 field inside the subject, which is called transmitting. The induced current in an RF coil is generated by the magnetization (M) in the imaged object, and this phenomenon is called receiving. Much works have shown that the quality of the image obtained by MRI is, in particular, depending on the intensity of the homogeneity of radiofrequency fields (RF) B1T produced by the transmit coil and B1R associated with the receiving coil (Anderson, 1999), (Bongiraud & Jeandey, 1999), (Harpen, 1991), (Mispelter & ANMR, 2006), In general, the homogeneity of the B1 field produced by the RF coils is in multiple radiating elements and their design is constantly optimized. We take into account the problems of inductive coupling between all elements (rings) so that to facilitate the design process due to the periodic geometry of structure
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